Purines phosphoribosylpyrophosphate

The first step of this sequence, which is not unique to de novo purine nucleotide biosynthesis, is the synthesis of 5-phosphoribosylpyrophosphate (PRPP) from ribose-5-phosphate and adenosine triphosphate. Phosphoribosyl-pyrophosphate synthetase, the enzyme that catalyses this reaction [278], is under feedback control by adenosine triphosphate [279]. Cordycepin interferes with thede novo pathway [229, 280, 281), and cordycepin triphosphate inhibits the synthesis of PRPP in extracts from Ehrlich ascites tumour cells [282]. Formycin [283], probably as the triphosphate, 9-0-D-xylofuranosyladenine [157] triphosphate, and decoyinine (LXXlll) [284-286] (p. 89) also inhibit the synthesis of PRPP in tumour cells, and this is held to be the blockade most important to their cytotoxic action. It has been suggested but not established that tubercidin (triphosphate) may also be an inhibitor of this reaction [193]. 

ThiolMP and ThioGMP are feedback inhibitors of phosphoribosylpyrophosphate amido-transferase, which is the first, and rate-limiting step in the synthesis of purine. In addition, these analogs inhibit the de novo biosynthesis of purine and block the conversion of inosinic acid to adenylic acid or guanylic acid. The triphosphate nucleotides are incorporated into DNA, and this results in delayed toxicity after several cell divisions. 

Fig. 4. Possible pathways of purine nucleotide anabolism and catabolism. The heavy arrows indicate the normal routes of degradation in man. I = phosphoribosylpyrophosphate, II = phosphoribosylamine, III = inosinic acid, IV = xanthylic acid, V = adenyhc acid, VI = guanyhc acid VII = hypoxanthine, VIII = xanthine, IX — uric acid, and X = adenosine.

J3. Jones, 0. W., Jr., Ashton, D. M., and Wyngaarden, J. B., Accelerated turnover of phosphoribosylpyrophosphate—a purine nucleotide precursor in certain gouty subjects. J. Clin. Invest. 41, 1805-1815 (1962). 

Purine synthesis starts with ribose-5-phosphate, which can be formed from the pentosephosphate pathway either via the oxidative arm or, in the reverse fashion, via the nonoxidative arm. Many tissues have the ability to form ribose-5-phosphate and their own purines. The first reaction is with ATP, where pyrophosphate is added to ribose-5-phosphate to produce phosphoribosylpyrophosphate (PRPP). 

Phosphoribosylpyrophosphate can be used in a number of reactions. It is important in the synthesis of purines, pyrimidine nucleotides, and coenzymes such as NAD+. Therefore, it would not be prudent for strict... 

FIGURE 23.24 Purine salvage, (a) Adenine is the purine in this example. There are analogous reactions for salvage of guanine and hypoxanthine (see page 697). (b) The formation of phosphoribosylpyrophosphate (PRPP). 

The rate-limiting enzyme in the synthesis of purine nucleotides is amidophosphoribosyl transferase (also known as phosphoribosylpyrophosphate amido transferase), which is a major target for one of the two thiol-containing purine anticancer antimetabolites on the U.S. market. 

Fig. 3. Reactions of purine recycling. ODC, ornithine decarboxylase ADA, adenosine deaminase HPRT, hypoxantUne phosphoribosyltransferase SAM, S> adenosylmethionine SAMP, adenylsuccinate PRibPP, phosphoribosylpyrophosphate.

G5. Green, C. D., and Martin, D. W., Jr., Characterization of a feedback-resistant phosphoribosylpyrophosphate synthetase from cultured, mutagenized hepatoma cells that overproduce purines. Proc. Nat. Acad. Set. V.S. 70, 3698--3702 (1973). 

Sperling, O., Boer, P., Persky-Brosh, S., Kanarek, E., and De Vries, A., Altered kinetic property of erythroc e phosphoribosylpyrophosphate synthetase in excessive purine production, flee. Eur. Etud. Clin. Biol 17, 703-706 (1972). 

Wingaarden, J.B. Ashton, D.H. (1959). The regulation of activity of phosphoribosylpyrophosphate amidotransferase by purine ribonucleotides a potential feedback control of purine biosynthesis. ]. Biol. Chem., 234, 1492-6. 

Holmes, E.W., Wyngaarden, J.B., and Kelley, W.N. Human glutamine phosphoribosylpyrophosphate amidotransferase Two molecular forms interconvertible by purine ribonucleotides and phosphoribosylpyrophosphate. J. Biol. Chem., 248 6035,1973. 

Wyngaarden, J.B. and Kelley, W.N. Gout with purine overproduction due to increased phosphoribosylpyrophosphate synthetase activity. In Gout and Hyperuricemia, Chapter 24, Grune Stratton, New York, 1976, pp. 301-308. 

No evidence for the presence of a known enzyme abnormality causing purine overproduction could be obtained. The erythrocyte activity of hypoxanthine-guanine phos-phoribosyltransferase (HGPRT), of adenine phosphoribosyltransferase (APRT), and of phosphoribosylpyrophosphate (PRPP) synthetase were all in the normal range. Erythrocyte PRPP generation, as well as the acitivity of the pentose phosphate pathway was also normal (Table 1). In addition, the rate of de novo synthesis of purine nucleotides in cultured skin fibroblasts from the patient was found to be normi. 

Keenly G.H.y Borkowskyy W.y and Hirschhorny R.y 1979y Purine and phosphoribosylpyrophosphate metabolism of lymphocytes and erythrocytes of an adenosine deaminse deficient immunocompetent childy Pediatr. Res.y 13 649. 

Becker et al recently reported a variant of the purine synthetic enzyme phosphoribosylpyrophosphate (PP-ribose-P) synthetase (EC 2.7.6.1) in a patient with symptoms characteristic of the Lesch-Nyhan syndrome at three years of age, but with normal HGPRT enzyme levels. The clinical manifestations of this X-linked disorder in three previous families in which it had been described had been restricted to gout, uric acid lithiasis and/or renal insufficiency and had not developed until early adulthood. ... 

The patient s RBC ADA activity was 43 000 nmol.min . ml RBC " (normal values 495 i 60), There was an about 3-fold increase of red cell pyrimidine 5 -nucleotidase and orotate phosphoribosyl-transferase, whereas other enzymes of purine and pyrimidine metabolism (inosine phosphorylase, adenosine kinase, adenine phosphoribo-syltransferase, hypoxanthine-guanine-phosphoribosyltransferase, phosphoribosylpyrophosphate synthetase) were normal or slightly elevated. There was a 6-fold increase of pyruvate kinase activity relatively to comparably reticulocyte-rich blood, and a 1.5 to 3-fold increase of the other enzymatic activities of glucose and glutathione metabolism. Plasma ADA was much elevated (30.5 pmol.min . ml normal value 5.1 - 2.5), probably reflecting intravascular hemolysis. ADA activity in lymphocytes (2.13 nmol.min 1.10 cells normal 1.93 0.61) and in fibroblasts (26 nmol.min l.mg protein 1 normal range 14-118) was normal, whereas the small increase of activity in platelets (59.5 nmol.min . 10 cells control 26.7) and in the liver (8.4 pmol.min . mg protein" normal ... 

Sperling, 0., P. Boer, S. Persky-Brosh, E. Kanarek, and A. de Vries. 1972. Altered kinetic property of erythrocyte phosphoribosylpyrophosphate synthetase in excessive purine production. Europ. J. Clin. Biol. Res. 17 703. 

Becker, M. A., L. J. Meyer, A. W. Wood, and J. E. Seegmiller. 1973. Purine overproduction in man associated with increased phosphoribosylpyrophosphate synthetase activity. Science 179 1123. 

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